The gastrointestinal (GI) tract is a major target of HIV/SIV infection and CD4+ T cell depletion. The damage to the mucosal immune system is associated with a variety of GI manifestations collectively called AIDS enteropathy; generally characterized by chronic diarrhea, and wasting. Although our understanding of HIV/SIV enteropathy has greatly improved lately, the recent discovery of microRNAs (miRNAs) has added yet another novel and complex regulator of gene expression with potential roles in the molecular pathogenesis of this disorder. miRNAs are ~21-23 nucleotide noncoding RNAs, highly conserved and suppress gene expression by targeting mRNAs for translational repression or degradation. While miRNA studies are being reported extensively in various types of cancer, and at increasing rates in cardiac, neurological, metabolic and skin diseases, their role in idiopathic GI disorders such as HIV/SIV enteropathy is unknown and yet to be addressed. Preliminary Locked Nucleic Acid-based miRNA microarray profiling of colon tissue from SIV-infected macaques with chronic diarrhea and wasting revealed significant deregulation in the expression of several miRNAs. Based on our strong preliminary evidence, we hypothesize that miRNA expression is deregulated in the GI tract consequent to HIV/SIV infection and that this contributes to disruption of enteric structure and function (AIDS enteropathy). The broad goals of this study are to 1a.) Identify genome wide temporal changes in miRNA expression (microarray and miRNA cloning) in the GI tract in response to SIV infection and determine if expression signatures specific to pathogenic events such as immune activation, inflammation, and epithelial barrier disruption can be identified 1b.) Further corroborate all miRNAs showing differential expression using real-time RT-PCR. 1c.) Determine cellular localization of differentially expressed miRNAs (in situ hybridization/immunofluorescence) in the colon and verify if differences in expression exist between cell types in close proximity 2.) Determine the functional significance of the inflammation associated miR-212 by validating its putative protein targets (mass spectrometry) in the intestinal epithelium and in in vitro cultured primary intestinal macrophages. Understanding the role of miRNAs and their putative target genes/proteins will provide important insights into the pathogenesis of HIV/SIV enteropathy and, possibly, other GI inflammatory conditions. Molecular mechanisms uncovered through these studies may open new miRNA-based strategies for the diagnosis and treatment of idiopathic GI disorders like AIDS enteropathy.